It is well known to form an image by phase contrast imaging methods in which phase modulation of light is converted into intensity modulation. As opposed to intensity modulation, phase modulation does not involve loss of energy.
A generalized phase contrast imaging method and system is disclosed in International Patent Application Publication No. WO 96/34207 for synthesizing a prescribed intensity pattern. The generalized method is not based on the so-called Zernike approximation that the phase shift φ is less than 1 radian. An improved method is provided without this assumption and based on an imaging operation with a simple one-to-one mapping between resolution elements or pixels of a spatial phase modulator and resolution elements of the generated intensity pattern.
The disclosed phase contrast imaging method of synthesizing a prescribed intensity pattern I(x′,y′), comprises the steps of:                dividing the intensity pattern I(x′,y′) into pixels in accordance with the disposition of resolution elements (x,y) of a spatial phase mask having                    a plurality of individual resolution elements (x,y), each resolution element (x,y) modulating the phase of electromagnetic radiation incident upon it with a predetermined phasor value eiφ(x,y),                        radiating electromagnetic radiation towards the spatial phase mask,        Fourier or Fresnel transforming the modulated electromagnetic radiation,        phase shifting with a spatial phase filter (SPF) in a region of spatial frequencies comprising DC in the Fourier or Fresnel plane, the modulated electromagnetic radiation by a predetermined phase shift value θ in relation to the remaining part of the electromagnetic radiation, and        forming the intensity pattern by Fourier or Fresnel transforming, respectively, the phase shifted Fourier or Fresnel transformed modulated electromagnetic radiation, whereby each resolution element (x,y) of the phase mask is imaged on a corresponding resolution element (x′,y′) of the image,        calculating the phasor values eiφ(x,y) of the phase mask and the phase shift value θ in accordance withI(x′,y′)=|eiφ(x′,y′)+ α(eiθ−1)|2         for selected phase shift values θ, α being the average of the phasors eiθ(x,y) of the resolution elements of the phase mask,        selecting, for each resolution element, one of two phasor values which represent a particular grey level, and        supplying the selected phasor values eiφ(x,y) to the resolution elements (x,y) of the spatial phase mask.        
In one embodiment disclosed in WO 96/34207, the spatial phase mask is positioned at the front focal plane of a lens while the spatial phase filter is positioned in the back focal plane of the lens, whereby a first electromagnetic field at the spatial phase mask is Fourier transformed by the lens into a second electromagnetic field at the spatial phase filter. Thus, specific spatial frequencies of the first electromagnetic field will be transmitted through the spatial phase filter at specific positions of the phase filter. For instance, the energy of the electromagnetic radiation at zero frequency (DC) is modified by the phase filter and transformed onto the intersecting point of the Fourier plane and the optical axis of the lens also denoted the zero-order diffraction region.
Typically, the spatial phase filter is adapted to phase shift the DC-part of the electromagnetic radiation and to leave the remaining part of the electromagnetic radiation unchanged. Alternatively, the DC-part of the electromagnetic radiation remains unchanged and the remaining part of the electromagnetic radiation is phase shifted. This alternative is preferred when the energy level of the DC-part of the electromagnetic radiation is so high that the phase shifting part of the phase filter will be destroyed by it. For example in laser cutting, the DC level of the laser beam can be so high that a phase shifting dot positioned at the intersecting point of the DC part of the laser beam at the phase filter would deteriorate. It is also possible to block the electromagnetic radiation (no transmittance) in the zero-order diffraction region, however, the DC energy of the radiation is then lost.
In US 2003/0030902 a microscope system is disclosed for obtaining images of optimum image quality comprising 1) an illuminating device which emits light from a light source to an object, and generates a luminous flux including information of the object, 2) an illuminating light modulating device which modulates at least one of wavelength, phase, intensity, polarization, and coherency of the light emitted to the object by the illuminating device, 3) an objective lens and an imaging lens which focus the luminous flux including the information of the object to form the image of the object, 4) a pupil modulating device which is disposed near a pupil plane of the objective lens, and modulates at least one of phase, intensity and direction of polarization of the luminous flux including the information of the object, 5) an image pickup device which is disposed on a plane on which the image of the object is formed by the objective lens and the imaging lens, and picks up the image of the object, 6) an image display device which displays the image of the object picked up by the image pickup device, 7) an image analysis device which analyses the image of the object picked up by the image pickup device, and 8) a parameter decision device which adjusts the modulation amounts of the illuminating light modulating device and the pupil modulating device by using the image information of the object analysed by the image analysis device.
The pupil modulating device is a phase filter and in one of the disclosed embodiments (FIG. 7) the phase shift is equal to
  π  2and the phase shifting area of the phase filter is annular. In another of the enclosed embodiments (FIG. 9) the phase shift is equal to π and the phase filter is divided into a plurality of rows, every second row having phasor value eiπ and being interlaced with the remaining rows having the phasor value ei0.
US 2003/0030902 does not disclose a method of synthesizing an intensity pattern by designing a phase modifying element with phasor values eiφ(x,y) calculated from intensity values of the desired intensity pattern. In US 2003/0030902, the phase modifying element is a sample that is obtained for studying it in a microscope. The sample is not designed with the purpose of generating a certain intensity pattern.